There has been an increasingly distinct contradiction between an increasing demand for broadband radio communication and a limited amount of spectrum resources along with rapid development in the industry of mobile communications, and although Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO) and other technologies have been adopted in the Long Term Evolution (LTE), these have failed to address the problem of the limited amount of spectrum resources thoroughly.
Telecommunication operators will be faced with a more serious problem of the scarce spectrum resources along with rapid development of mobile services in future, and on the other hand, the spectrum use of some radio systems has been almost left idle temporally and geographically, for example, many of radio and television bands have been left idle all the time because a transmission capacity can be improved greatly by digital transmission along with evolvement of radio and television systems from analog transmission to digital transmission, thus wasting the precious radio resources, whereas many of the other radio systems have also been proved to have their spectrums underutilized.